1. Field of the Invention
The present invention relates to a silicon thin film structure for optoelectronic devices employed in optical communication fields. More specifically, the present invention relates to a silicon thin film structure for optoelectronic devices comprising a silicon/silica superlattice structure as a basic backbone, which has excellent luminescence efficiency, by doping an erbium element in a silica layer, or interposing a pure silica layer between a silicon layer and an erbium-doped silica layer, or adjusting thickness of a silicon layer in the silicon and erbium-doped silica superlattices, and a method for manufacturing the same.
2. Description of the Prior Art
Generally, optoelectronic devices have been fabricated by use of semiconductors of Group III-V compounds. However, the integration process of the semiconductors into single chips is difficult because of definitely different chemical properties between Group III elements and Group V elements, as recognized from the fact that, since the first success in the development of silicon-based integrated electronic devices, various efforts have been made to substitute other Group III-V compounds having more excellent physical properties (faster in the mobility of electrons and holes on a silicon base) for the conventional ones, but failed to fabricate devices with faster response speed. However, as with electronic devices whose functions advanced rapidly after their integration, electronic devices will likely be successfully integrated in the very near future, thereby raising expectations of greater advances in this field.
Luminescence can be easily obtained from semiconductors of Group III-V compounds, but they are difficult to be integrated. By contrast, silicon can be integrated, but do not emit light owing to indirect band gap in the crystalline structure phase of silicon. There have been. devised various methods for emitting light from silicon. One of them is to dope luminescent materials to silicon. As the luminescent materials, rare-earth elements were suggested. Of them, erbium has been under vigorous study. The reason is that erbium emits light with a wavelength of 1.54 xcexcm, which shows the lowest optical absorption rate in optical fibers in current use in the optical communication fields and consequently, has the advantage of being low in light loss. Already, light-emitting diodes using erbium-doped silicon have been fabricated, but not developed to practical use because of low luminescence efficiency. To circumvent this problem, erbium and nanocrystalline silicon are doped into silica, thus raising the luminescence efficiency. The doping of Er and Si nanostructures into silica experiences difficulty in controlling the number and size of nanostructures and the location of erbium. In order to emit light, erbium must receive energy from the nanocrystalline silicon and not transmit the energy back to the nm-thin silicon. In other words, to increase erbium luminescence, erbium and silicon should be present at such locations relative to each other as not to back-transmit energy transmitted from the nanocrystalline silicon. But, it is highly difficult to control the location of erbium and silicon. Moreover High electric conductivity is required for performing electric excitation in electroluminescence device. However, the silica film as thick as 1 micron or more, even though containing nanocrystalline silicon therein, suffers from the disadvantage of being very poor in electric conductivity.
Accordingly, an object of the present invention for alleviating the problems as described above is to provide a silicon thin film structure for optoelectronic devices, which have increased luminescence efficiency and high conductivity, and a method for manufacturing the same.